Role of ABA, salicylic acid, calcium and hydrogen peroxide on antioxidant enzymes induction in wheat seedlings

Experiments were conducted to study the regulatory role of salicylic acid (SA), abscisic acid (ABA), calcium (Ca2+) and hydrogen peroxide (H2O2) on antioxidant enzymes induction in wheat genotypes C 306 and Hira. Results revealed that SA (1 mM), ABA (0.5 mM), Ca2+ (5 mM) and H2O2 (0.05 mM) were most effective in increasing the activities of superoxide dismutase (SOD), ascorbate peroxidase (APOX), catalase (CAT) and NADPH oxidase. Hydrogen peroxide contents estimated immediately after termination of treatments also increased by all the treatments. The response was more with Ca2+ + ABA, followed by Ca2+ alone, both in terms of antioxidant enzymes and H2O2 contents. EGTA, a calcium chelator, decreased the activity of all the antioxidant enzymes below control level as well as decreased H2O2 contents. Similarly, DPI, a specific inhibitor of membrane linked NADPH oxidase, not only inhibited NADPH oxidase activity, but also inhibited the increase of SOD and APOX activity. Results revealed that SA induced H2O2 accumulation in germinating seedlings was not associated with inhibition of CAT or APOX. It is suggested that abiotic stress signal is transduced via ABA, Ca2+ and H2O2, which might be responsible for the activation of some common transcription factor associated with SOD, APOX and CAT.